Currently, the two main methods known for water desalination are reverse osmosis (RO) and multiple effect distillation (MED). These methods can be expensive; typically, large-scale RO systems produce clean water at a cost of between $1.50 and $2.00 per cubic meter, and MED systems produce clean water a cost of between $0.70 and $1.50 per cubic meter. As a result, small or cash-strapped communities are often unable to pursue desalination to meet their needs for clean water and are forced to rely on other sources, which may have more pronounced environmental consequences.
In addition, RO and MED themselves have a number of environmental and economic drawbacks. Many RO and MED plants emit concentrated brine as a waste product; this brine can be toxic to the marine environment in the surrounding area. RO and MED systems are also notoriously fragile and unreliable, and often shut down even when only a single part fails. RO has a particularly strong negative effect on environment because it relies on filter membranes, the manufacture of which creates industrial wastes, and requires significant quantities of electrical power. MED uses less electrical power than RO, but requires a steam source in addition to an electrical source; many methods of generating steam have severe environmental impacts.
There is thus a need for systems and methods of water purification that do not emit a concentrated brine solution into the surrounding environment, but preferably utilizes the waste brine productively. It is advantageous for such systems and methods to utilize inexpensive, easily acquired components to produce clean water at the lowest possible cost, and to produce few or no toxic after-products. It is further advantageous for such systems to be designed robustly, such that the system can continue to operate despite the failure of a single component or subsystem, and to be effective for both desalination and remediation of dirty water.